Multiple sheet detector



E. R. KOLB I MULTIPLE SHEET DETECTOR May 4, 1965 Filed Nov. 21, 1960 4 Sheets-Sheet 1 INVENTOR [aw/ fi K015 BY IMO M%w ATTORNEYS May 4, 1965 Filed Nov. 21, 1960 E. R. KQLB 3,132,301

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ATmRNEYS R\ W m Q Q g E4 1P w: E A .5 mg NE E wk U m5 QE V H 4 [ow/N lP. K045 vb QU M w J Hr m5 a; m. v s l i B 1% w a v E x Qtq m& E J F {L 0 L w n ofi h? mm M 1 r y United States Patent 3,182,301 MULTIPLE SHEET DETECTOR Edwin R. Kolb, University Heights, Ohio, assignor to Harris-Intertype Corporation, Cleveland, Ohio, a corporation of Delaware Filed Nov. 21, 1960, Ser. No. 70,592 20 Claims. (Cl. 340259) The present invention relates to sheet-handling machines wherein a stream of sheets is established to suecessively supply individual sheets to a predetermined position, and which has detecting means for sensing when the sheets arrive at the position, or the thickness of the sheet arriving at the position, or both, and for performing a control operation when the sheets are improperly delivered.

Sheet-feeding machines of the stream type are commonly used with printing presses and, when so used, the sheets of the stream successively move to a registering position, from which they are taken and delivered to the printing press. The sheets of the stream may be separated from each other so that the sheets are not overlapped or the stream may be a lapped stream comprised of either overlapped or underlapped sheets. For printing presses and certain other machines for operating on sheets received from the stream, it is important that only one sheet at a time move to a position from which it is taken into the machine or press and that the sheets arrive in proper time with respect to the operation of the printing press or other sheet-handling machine.

An important object of the present invention is to provide a sheet-handling machine in which sheet material advances as part of a stream of sheets past a sensing position at which sensing means, which is responsive to the change in thickness of the stream moving by the station, operates to indicate that the leading edge of a sheet has arrived at the station or to indicate the thickness of the arriving sheet, or both, and wherein control means is responsive to an increase in thickness of the stream for performing a control operation when the change in stream thickness corresponds to more than that of a single sheet thickness, or when the change in thickness indicating the arrival of the leading edge of the sheet at the sensing station occurs out of time, or both, the control means being so constructed and arranged that it is only responsive to changes in thickness of the stream.

Another object of the present invention is to provide a new and improved sheet-handling machine in which sheets advance in succession along a table as part of a stream of lapped sheets and in which the movement of an edge of sheet material past a sensing position is detected by sensing means including an element which is deflected in response to the arrival or" the edge, or the thickness of sheet material as the leading edge moves by the sensing station, the operation and indication of the sensing means being substantially independent of the thickness of other sheet material of the stream at the sensing station and located between the arriving sheet and the defiectable element.

Still another object of the present invention is to provide a new and improved method and apparatus for checking the movement of sheets in a stream, in which means the sheets moving into a predetermined position effect the actuation of pulse-producing means to provide pulses which may be analyzed to determine whether the sheets are present and in time or whether the thickness of the sheet is such to indicate a double sheet, or both.

Yet another object of the present invention is to provide a new and improved method and apparatus as in the next preceding object wherein the pulses have a magnitude 3,132,301 Patented May 4, 1965 dependent on sheet thickness and are analyzed both as to magnitude and time to determine whether or not the sheets are arriving properly at the position.

It is also an object of the present invention to provide a new and improved sheet-handling apparatus wherein sheets are moved in succession to a first position and advanced to the position as part of a stream of lapped sheets and which is so constructed and arranged that the movement of an edge of sheet material advancing to the first position will be sensed as it passes a sensing position and the thickness of the sheet material moving to the first position indicated even though the sheet material is overlapped by other sheet material at the sensing position.

A further object of the present invention is to provide a new and improved sheet-handling apparatus for successively delivering individual sheets to a predetermined position in synchronism with the operation of related apparatus, such as a printing press, in which sheet-hair dling apparatus pulses are derived in response to changes in thickness of sheet material moving to the position and are compared with clock pulses synchronized in time with the apparatus to indicate out of time or absent sheets and wherein the pulses derived from the sheet material have a magnitude which is a function of sheet thickness and are analyzed to determine the presence of an excess number of sheets.

A still further object of the present invention is to provide a new and improved sheet-handling apparatus for successively delivering sheets to a position wherein the sheets are to be front and side registered and wherein pulses are derived from the sheets as they move to the position by a device which does not interfere with the front or side registering operations and which includes a member adjacent the sheet and deflected as the leading edge moves thereby.

Yet another object of the present invention is to provide a new and improved sheet-handling apparatus wherein sheets moving to a predetermined position effect the displacement of a deflectable member to provide an output signal having a magnitude which is a non-linear function of the displacement and wherein the output signal is utilized to provide a further signal which has an adjustable magnitude for a given magnitude of displacement of the defiectable member and a magnitude which varies directly with displacement, the latter signal being analyzed to determine whether or not more than a predetermined number of sheets effected the displacement of the deflectable member.

Further objects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiment thereof made with reference to the accompanying drawings forming a part of the specification and in which:

FIG. 1 is a sectional view, somewhat diagrammatic, illustrating a sheet-handling machine embodying the present invention and including sensing means for detecting the movement of the individual sheets of a stream of sheets to a predetermined position;

FIG. 1A is an enlarged portion of FIG. 1 showing a sheet arriving at the transducer of the sensing means;

FIG. 2 is a graph showing the output or" the sensing means of FIG. 1 when a lapped stream of sheets moves by the sensing station;

FIG. 3 is a block diagram of the sensing means and associated control apparatus;

FIG. 4 is a circuit diagram of means;

FIG. 5 is a circuit diagram of part of the sensing means and of the control means responsive to the sensing means;

part of the sensing FIG. 6 is a simplified showing of the adder circuit used in the illustrated embodiment;

FIG. 7 is a modified form of control circuit embodying the present invention;

FIG. 8 is still another modified form of control circuit.

FIG. 9 is an enlarged view of a portion of FIG. 1 of operation of a portion of FIG. 1 when relatively stiff sheets are being handled; and

FIG. 10 is an illustrative view corresponding to FIG. 9 showing the manner of operation in the absence of a part of FIG. 9.

In accordance with the present invention, the sheethandling machine of the stream-feed type has sensing means for sensing the individual sheets of the stream as the sheets move to a predetermined position. The sensing means responds to the change in thickness of the sheet stream at the sensing station as an edge of a sheet passes the station. Preferably, the leading edge of the sheet of the stream displaces an element whose position controls the magnitude of an electrical signal, and the displacement of the element produces a change in the signal and this change is utilized to provide a pulse which preferably has a magnitude which is dependent upon the magnitude of the edge of the sheet material that has advanced to sensing position. In the preferred and illustrated embodiment, the element which is displaced by the leading edge of the sheet or the change in thickness of the stream due to the arrival of the leading edge of the sheet, is a member of ferromagnetic material and is associated with a coil and when the ferromagnetic member is displaced, the inductance of the coil is varied to vary the signal strength in a signal circuit which includes the coil as a part thereof. According to one feature of the invention, the time of the change in signal strength due to the arrival of the leading edge of the sheet is compared with a clock pulse which occurs in time corresponding to the proper time for the arrival for the sheet. The clock pulses are preferably derived from a member which is operated synchronously with the sheet-handling machine so that changes in speed of the sheet-handling machine will also eifect the necessary change in the clock pulses and the pulse generator for the clock pulses may comprise a slotted disk driven from the drive for the machine and controlling the transmission of light between a light source and a photocell. The disk may have a single slot therein and be rotated once for each sheet to be fed so that each time the slot passes between the light and the photocell, a pulse is derived at the time a sheet is due to arrive at the sensing station. If the signal from the sensing apparatus occurs in time with the pulse from the disk, the arrival of the sheet at the sensing station is in time. Inaccordance with another feature of the invention, the magnitude of the change in signal upon the arrival of the leading edge of the sheet is a function of the thickness of the leading edge so that the magnitude of the change in signal can be analyzed to determine whether a single sheet or a double sheet has arrived at the sensing station. In the preferred embodiment, a pulse is derived from the change in signal and this pulse is applied to an adding circuit whose output effects the actuation of a control function. The pulse applied to the adding circuit is of the necessary sense and polarity to effect the control operation. The control circuit, however, includes additional circuit means to which both the pulses from the sensing means and the clock pulses are applied, and if both a sensing pulse and a clock pulse are applied to the additional circuit means, a pulse of opposite sense to the sensing pulse from the sensing means is applied to the adder to cancel the sensing pulse so that no control operation is effected. If, however, the pulse from the sheet-sensing means is applied to the circuit means at a time other than a time coinciding with a clock pulse, no output pulse from the circuit means will be applied to the adder and the control operation will be effected. The control operation will also be effected if the magnitude of the pulse from the sheet-sensing means is such that the magnitude of the pulse signal from the additional circuit means does not effectively cancel the sheet pulse. In the preferred embodiment, if the pulse tom the sheet-sensing means is due to a thickness of two sheets, its magnitude is such that it will effect the control operation even though it occurs in time with a clock pulse.

Referring to the drawings, the present invention is shown as embodied in a sheet-handling machine comprising a feedboard 10 on which a stream of sheets, a stream of underlapped sheets in the illustrated embodiment, moves to supply sheets in succession to a front register position adjacent the front edge of the feedboard it where the sheets are successively registered against a plurality of front stops distributed across the feedboard adjacent its forward edge and including a front stop 11. After engaging the front stops, the sheet is side registered by side-registering mechanism 12 and then moved from the front register position to a cylinder 13 of a printing press. The side-registering mechanism 12 may be of any suitable conventional type. The sheets are advanced from the front register position to the cylinder by feed rolls including a feed-roll segment 14. The front stops are positioned in cutouts, including cutout 15, in the front edge of the feedboard and are movable from a position in the path of a sheet moving down the feedboard, as is shown in FIG. 1, to a position below the surface of the feedboard when the feed rolls are to be operated'to advance the sheet in the registered position to the cylinder 13. The cylinder 13 includes gripper means 16 which receive the sheet and carry the sheet into the printing press.

As the sheet is gripped by the gripper means 16 and is being pulled from the feedboard 10, the next sheet is advancing underneath the sheet being pulled by the cylinder and the front stops are raised to front register the sheet, and this front registration occurs, in the type of feeder shown, before the tail of the sheet being pulled by the cylinder 13 clears the front stops 11. if desired, overguide means 18 may be provided in addition to the front stops to catch any sheet which might tend to pass the front stops and to lift the tail of the sheet being advanced to the cylinder 13. Both the overg-uicle means 18 and the front stops are conventional mechanisms and are reciprocated in the known manner between active and inactive positions, and' the mechanism for effecting the reciprocation will not be described since it does not per se form a part of the present invention. As the sheets of the stream move to the front register position against front stops 11, the sheets pass a sheet-sensing station 23 at which a transducer T detects a change in the thickness of the stream due to the arrival of the leading edge of a sheet. The transducer at the sensing station 23 also senses the change in thickness due to the. passage of a trailing edge of a sheet but this sensing is ignored by the control circuit, as will be apparent from the description set forth hereinafter.

In the preferred and illustrated embodiment, the transducer T at the sensing station includes a ball 24 of ferromagnetic material which rides on the top of the stream of sheets at the sensing station 23. In the preferred embodiment, the ball rides in a cylindrical guide 24a which is open at the end adjacent the table and the ball is urged toward the table by a spring 24b. It will be noted that the ball 24 will have little or no tendency to interfere with the movement of the sheet in any direction,

including a forward direction and a side direction. The table immediately below the ball 24 has an opening 25 therein in which a ramp 2r) is positioned so that the table it has a hump or rain-p immediately opposite the ball 24 and arranged so that the leading edge of a sheet moving along a table must ride up the ramp. The ramp 26 is of nonmagnetic material and preferably a nonconduotor of electricity. A magnetic core 27 is disposed immediately below the ramp 26 and has a pair of windings 28, 29 thereon, the windings being connected in series relationship. The inductance of the windings 28, 29 depends upon the magnetic reluctance of the flux path for the coils. The core 27 is a circular core and has an air gap 31 immediately adjacent the ramp 26 and below the ball 24. Movement of the ball 24 toward and away from the core 27 will vary the reluctance of this air gap and will in turn vary the inductance of the coils 28, 29, as will be Well understood by those skilled in the art.

The coils 28, 29 are part of a bridge circuit 30. The bridge circuit 30 also includes a center-tapped secondary coil 33 of a transformer 34. The secondary coil 33 has coil portions 33a, 331) on opposite sides of the center tap. The transformer 34 also includes a primary coil 35 energized by an oscillator 36.

The end terminal of the coil portion 33a is connected to a bridge junction 37 through the inductance coils 28, 29 and the outer end of the coil portion 33b is connected to the junction 37 through a variable resistor 38 and a variable inductance 40 in series with the coil portion 33b. The primary coil 41 of an output transformer 42 is connected between the center tap of the secondary coil 33 and the junction 37. It will be recognized that the circuit described is a bridge-type circuit energized by the oscillator 36 and that it would be possible to balance the magnitudes of the inductances and resistance of coils 23, 29 and that magnitude of inductance 40 and resistor 38 so that no voltage output appears across the center tap of the secondary transformer 34 and the junction 37. Then, if the inductance of the coils 28, 29 were changed, a voltage would appear. Preferably, the circuit is in an unbalanced condition so that a signal voltage normally appears across the primary 41 of the output transformer 42, and this signal voltage is changed or modulated as the ball 24 is displaced to change the inductance of the coils 2-8, 29. Preferably, the bridge is unbalanced in such a manner that when the inductance of the coils 2d, 2d decreases as the ball 24 moves away from the core, the magnitude of the signal applied to the primary 4-1 decreases to decrease the magnitude of the signal appearing at the secondary coil 43 of the output transformer 42.

In the described type of transducer, the variation of the inductance of the coils 28, 29 will be a non-linear function of the position of the ball 24 with respect to the coils, and core 27. I have discovered that this nonlinear function will, however, for a certain range of positions of the ball 24 vary logarithmically with the position of the ball. In the illustrated and preferred embodiment, the spacing between the ball 24 and the core 27 is chosen so that as the ball 24 is moved, the output signal appearing at the secondary 43 of output transformer 42 will vary as a logarithmic function of the ball position.

The output signal from the transformer 42 is, as shown in the block diagram of FIG. 3, amplified by an amplifier i and then demodulated by a demodulator 46 to provide a direct current signal which varies logarithmically in accordance with the displacement of the ball 24. The output of the demodulator 4-6 is connected to an antilog circuit 47 which has an output that is the antilog of the input to the circuit. The output of the antilog circuit 47 is applied to the input of the variable-gain amplifier 48 which may include an inverting and amplifying stage for inverting the signal. The output of the variable-gain amplifier 48 is a differential output and appears as a pulse which occurs whenever the ball 24 is displaced, as when the leading edge of a sheet moves between the ball 24 and the ramp to change the thickness of the stream between the ball and the ramp. The output of the variablegain amplifier 48 is a positive going pulse signal, as is explained in more detail hereinafter. A negative pulse will also appear when a trailing edge of a sheet moves past the ball 24 and the stream thickness changes as a result thereof. The trailing edge pulse will be of opposite sense to the leading edge pulse and is ignored by the ci-rcuitry, as will become apparent hereinafter.

It can be seen that the elements described thus far provide sensing circuit means which operate to provide a pulse signal in response to a change in thickness of the stream. When the thickness increases, as in the arrival of a leading edge, a positive going pulse is provided and when a trailing edge passes the ball 24, a negative going pulse results at the output of amplifier 48, as is shown in FIG. 2. However, as will be apparent from the description hereinafter, the negative pulses are ineffective since the circuitry following the amplifier 48 effectively re sponds only to positive going pulses from the amplifier. In FIG. 2, the pulses have been identified as corresponding to successive sheets S of a stream by applying the reference character S to the pulse with an appended number representing the number of the sheet following the arbitrarily selected sheet No. 1.

The pulse from the variable-gain amplifier is applied to an adding circuit 50 and the adding circuit 50 will normally have one output on an output connection 51 and will have a different output whenever a positive pulse from the amplifier 48 is applied thereto unless a subtract pulse of opposite sense and magnitude is also applied to an input connection 52 to the adder. A one-shot or monostable multivibrator circuit 53 has an output connected to the connection 52 and when triggered from its stable to its non-stable state, will provide a pulse, a negative pulse in the illustrated embodiment, on the output connection 52 which is of a magnitude and shape to effectively cancel the pulse from the variable-gain amplifier if these pulses occur simultaneously. The one-shot multivibrator 53 has an input connection 54 to which the triggering signal for the multivibrator is applied. The connection 54 is connected to the output of an amplifier 56 and to the output of a multivibrator circuit 57 which is preferably a Schmitt trigger circuit. The multivibrator 57 is triggered from its normal state to its second state by the pulse appearing at the output of the variable amplifier 48 which is connected to an input 58 for controlling the multivibrator 57 as well as to the adder 59.

The amplifier 56 provides a clock pulse on the input connection 54 to the one-shot multivibrator 53 each time that a slotted disk 60 is rotated to a position wherein a slot 61 in the disk allows light to pass from a light source 62 to a photoelectric cell 63. The photoelectric cell 63 is connected to the input of the amplifier 56 and when subjected to the light of the light source 62, a positive pulse or step appears at the output of the amplifier 56.

The one-shot multivibrator 53 is of the type which is responsive to positive pulses and requires a positive pulse of a predetermined magnitude to effect a triggering from its stable state. The pulses from the one-shot multivibrator 57 and the amplifier 55 are such that only one pulse by itself is incapable of triggering the one-shot multivibrator 53, ie the pulses from the amplifier 56 and the pulses from the multivibrator 57 have magnitudes below the predetermined magnitude necessary to trigger the multivibrator 53, but the combined magnitudes have a magnitude greater than the magnitude necessary to trigger the one-shot multivibrator 53. Consequently, when the pulses occur during the same time interval or overlap, the one-shot multivibrator 53 will be triggered to supply a subtract pulse to the adder 50.

It can be seen that the present invention provides a means for determining whether or not the sheets are arriving at the proper time in the cycle of the machine. The slotted disk 60 is rotated in timed relation to the operation of the sheet-handling machine and at a rate such that the slot 61 is disposed between the light source 62 and a photoelectric cell 63 each time that the leading edge of a sheet is to be passing the sensing station 23. As explained previously, the leading edge of the sheet will cause a pulse signal to appear at the output of amplifier 48 when the leading edge displaces the ball 24 and this pulse will be applied to the adder 50 as well as to the one-shot multivibrator 57 which, in turn, applies a pulse signal to the input of the one-shot multivibrator 53. If there is a pulse at the output of the amplifier 56 when the pulse from the multivibrator 57 1s applied to the connection 54, the one-shot multivibrator 53 will be triggered to provide a subtract pulse to the adder S and no output signal will appear at the output of the connection 51. If, however, the slot 61 is not opposite to the light 62 when the pulse appears at the output of the amplifier 48, the one-shot multivibrator 53 will not be triggered and the pulse appearing at the output of the amplifier will not in effect be cancelled and an output signal will appear on the connection 51 from the adder. This output signal is utilized to trigger a multivibrator circuit 65 which controls a latching relay 66 for eifecting a tripping of the press. In the illustrated embodiment, the circuit 65 is of the Schmitt trigger type.

As hereinbefore mentioned, the pulses from the oneshot multivibrator 53 and the variable-gain amplifier 48 will in effect cancel themselves in the adder circuit 50 only if the pulses are of the same magnitude or if the difference in magnitude of the pulses is such that the output from the adder is not sufficient to trigger the multivibrator 65. Preferably, the pulses have the same magnitude when the displacement of the ball 24 is that corresponding to the thickness of a single sheet of material. When this is the case, if two sheets are proceeding down the feedboard together, the displacement of the ball 24 by the leading edges thereof will be twice that of a single sheet and the pulse from the variable-gain amplifier 48 will have a magnitude twice that of the pulse which occurs when the displacement is due to a single sheet. Accordingly, the subtract pulse from the one-shot multivibrator 53 will subtract only half of the pulse due to the sheets and the output pulse from the variable-gain amplifier be effective to produce an output signal on the connection 51 which will effect a triggering of the multivibrator 65 to energize the latching relay 66.

The various components of the sensing circuit for producing a pulse having a magnitude dependent upon the thickness of a leading edge of a sheet of a stream of sheets arriving at the sensing station 23 and the components of the control circuit responsive to the pulse may take many different forms, as will be appreciated by those skilled in the art. In the preferred and illustrated embodiment, the amplifier 45 which is connected to the output of the secondary coil 43 of the output signal transformer 42 comprises a triode 70 (see FIG. 4). The secondary coil 43 is connected between the grid of the triode 70 and ground, which is the negative side of the power supply for the amplifier. The plate of the amplifying triode 70 is connected to the positive side of the power supply through a plate resistor 71 and the output from the amplifier is taken from the plate of the triode and capacitively coupled by a condenser '72 to the demodulating circuit 46. The demodulating circuit 4s comprises a pair of rectifying diodes 74, 75 connected in parallel circuits between the condenser 72 and ground with the diodes being poled to conduct in different directions. The diode '75 is connected between the condenser 72 and ground in series with a condenser 76, the latter being connected between the diode 75 and ground, and the diode 75 is poled to conduct current from the condenser 72 to ground. The positive side of the condenser 76 is connected to the grid of a triode '78 of the antilog circuit 47, the connection being made through a resistor 80. This circuit has characteristics such that when a positive signal is applied to condenser 76, the voltage of the plate of triode 78 varies as an antilog function of this input voltage. Such circuits are well known in the art. The output of the triode '78 is taken from a junction 82 connected to the plate of the triode and varies in a manner dependent upon the displacement of the ball 24, and the output is a DC. signal.

The output of the antilog circuit 47 is connected to the input of the variable-gain amplifier 48 which is, in the preferred embodiment, a two-stage amplifier having a first stage comprised of a triode 85 having a grid which is connected to the junction 82. The plate of the triode 85 is connected to the power supply by a plate resistor 87 and a condenser 88 connected in parallel therewith. The output from the amplifying triode $5 is taken from a junction 00 between the plate resistor 87 and the plate of the triode and this junction is capacitively coupled by a condenser 92 to the grid of a triode 93 comprising the second amplifying stage of the amplifier 48. The cathode of the triode 93 is connected to ground through series connected resistors 94, 95 with the resistor 94 being connected to the cathode of the triode 93 and the resistor 95 being connected to ground. The grid of the amplifying triode is connected to a junction 96 between the resistors 94-, 95 by a grid-biasing resistor 97. The plate of the amplifying triode 93 is connected to the positive side of the power supply through a plate resistor 98 and two output junctions 100, 101 are provided in the connection between the plate resistor 98 and the plate of the amplifying triode 93.

It Will be recalled that the output of the antilog circuit is a DC. output obtained by demodulating the amplitude modulated carrier signal and the output of the amplifying triode 35 at the junction is a similar output but inverted. The time constant of the condenser 92 and associated resistors is such that the signal on the grid of tube substantially follows the output signal of triode 85. The signal at the output of the tube 90 is amplified and inverted by the triode 93 and the gain of the triode 93 is adjustable by varying the magnitude of the resistor 95 in the cathode circuit of the triode. The gain of the amplifier is adjustable for purposes which will be pointed out in more detail hereinafter.

The junctions 100, 101 of the plate circuit 40 of the triode 93 are connected to output terminals 103, 104 for the variable-gain amplifier 48. The connection between the junctions 100, 101 and the output terminals 103, 104, respectively, comprise a condenser 105 connected to the junction and a resistor a which connects the condenser to the output terminal 103 and a condenser 106 and a resistor 106a which connects the junction 101 to the terminal 104. The condensers 105, 105 and the series connected resistors are such to provide in effect a differentiating circuit such that relatively rapid changes in the output of triode 93 appear as pulses at the terminals 103, 104.

The output terminal 103 of the variable amplifier 4% is connected to a junction 118 of the adder 50 by a connection 108. The adder, as will be explained in more detail hereinafter, actually includes the resistor 105a as a part thereof and, in addition, includes resistors 109, 116. One side of the resistor 109 is also connected to the junction 11% and the other side thereof is connected through a rectifying diode 110 to a junction 111. The junction 111 is connected to the junction 118 by the resistor 116 and to a movable tap 112 of a potentiometer 113 having one end connected to the positive side of the power supply by a resistor 114 and its other end connected to ground, i.e. the negative side of the power supply, by a resistor 115. The potentiometer 112 and resistors 114, 115 provide a biasing voltage for the junction 118.

The adder circuit and its function will be described in more detail hereinafter.

The output terminal 104 of the variable-gain amplifier 48 is connected by the connection 58 to an input terminal for the multivibrator circuit 57 which is of the Schmitt trigger type. The Schmitt trigger circuit 57 is a conventional type of circuit and'includes vacuum tubes 121, 122 which are connected as a cathode coupled multivibrator circuit. The grid of the tube 121 is connected by a resistor 123 to a movable. tap 124 of a potentiometer 125 which is part of a voltage dividing circuit connected across the power supply. The position of the tap 124 determines the normal bias of the tube 121 and this tube is normally biased to cut oh. The plate of the tube 121 is connected to the positive side of the power supplied by a plate resistor 127 and to the grid of the tube 122 by a resistor 128 and a condenser 13% connected in parallel with the resistor 128. The grid of the tube 122 is also connected to ground through a grid resistor 131. The cathode of the tube 122 is connected to the cathode of the tube 121 and the cathodes are connected to ground through a common resistor 133. The plate of the tube 122 is connected to the positive side of the power supply through a plate load resistor 134. The circuit constants are such that the tube 121 is normally cut off and the plate thereof which is connected to the grid of the tube 122 is at a potential which maintains the grid 122 sufciently positive to maintain conduction of the tube 121. When, however, a positive voltage of a predetermined magnitude is applied to the grid of the tube 121, the tube 121 conducts, the plate voltage lowers, and the tube 122 is cut off to raise the plate voltage of the tube. When the voltage on the grid of the tube 121 drops sufiiciently, i.e. a little below the magnitude which causes conduction, the tube 121 will cease conduction, the plate voltage thereof will rise, and the tube 122 will be rendered conductive.

The plate of the tube 122 is capacitively coupled by a resistor 136 and a condenser 137 connected in series to the input of the one-shot multivibrator 53 to apply a positive pulse to the one-shot multivibrator 53 when the tube 122 ceases to conduct in response to a positive signal of a predetermined magnitude at the terminal 120. The input terminal for the one-shot multivibrator 53 has been designated by the reference numeral 138. The positive pulse from the Schmitt circuit 57 will effect a triggering of the one-shot multivibrator 53 if it occurs at the terminal 138 when a positive signal is present from the amplifier. 56. A positive signal or pulse occurs at the output of the amplifier 56 whenever the light from the light source 62 strikes the photocell 63 by passing through the slot 61.

The one-shot multivibrator 53 is comprised of two stages. One stage is provided by a gas tube 141) having a control grid 141 connected by a resistor 141a to the terminal 138 and a plate connected to the positive side of the power supply by a resistor 142. The cathode of the gas tube 140 is connected to a junction in a voltage dividing circuit 143 so that an adjustable voltage can be maintained at the cathode and the voltage of the cathode can be adjusted by varying an adjustable resistor 143a forming a part of circuit 143 and connecting the cathode of tube 141) to ground. The cathode voltage is adjusted so that the signalupon the Schmitt trigger circuit 57 or from the amplifier 56 cannot by itself fire the gas tube but so that the tube 141] will fire only if both signals are present. In addition to the gas tube 140, the one-shot multivibrator 53 comprises a triode 145 providing the second stage of the multivibrator. The triode 145 has its plate connected to the positive side of the power supply and its cathode connected to the negative side of the power supply through cathode resistors 146, 1 17 connected between the cathode and ground in the order named. The grid of the triode 145 is connected to the plate of the gas tube 140 by a resistor d and the plate of the gas tube and the grid of the triode 145 are connected to a junction between the cathode resistors 146, 147 by series connected resistors 152, 153. One end of the resistor 152 is connected to the plate of the gas tube 140 and one end of the resistor 153, which is a potentiometer type resistor having a movable tap 154, is connected to the junction between cathode resistors 146, 1 17. The bias on the triode 145 is normally such that the triode is conductive. When the gas tube 140 is fired, the plate voltage of the tube will drop and lower the bias on triode 145 to cut off the triode. The triode 145 will remain cut off as long as the tube 140 conducts. The gas tube 140 has a condenser 155 connected thereacross and upon the firing of the tube, the condenser discharges. When the condenser discharges to a predetermined level, the voltage across the plate and cathode will be insumcient to maintain the tube conducting and the tube 149 will cease conducting and the circuit will switch to its normal condition whence tube will again conduct in a time determined by resistor 142 and condenser 155. This type of circuit is well understood by those skilled in the art, as well as other types of monostable multivibrator circuits which have a stable state and a nonstable state of controlled duration and which can be used in the place of the disclosed circuit.

It will be appreciated that the plate of tube 140 is normally at a relatively high voltage, drops in voltage when the tube 140 fires, and returns when the tube 140 ceases conduction. The tap 154 follows this voltage swing and the tap is connected by a condenser 156 to a junction between the resistor 169 of the adder circuit and the diode 110. The resistor 199 and the condenser 156 diiferentiate the leading edge of the negative going output signal appearing at tap 154 to provide a negative pulse which is summed by the adder 50 of which the resistor 109 is also a part.

It can now be seen that when positive signals from both the Schmitt trigger circuit 57 and the amplifier 56 are applied to the multivibrator circuit 53, a negative signal is produced in the adder 50 in opposition to the positive signal from the variable-gain amplifier 48.

The junction 118 of the adder 50 is connected to the grid of a vacuum tube 160 forming a normally nonconducting stage of the Schmitt multivibrator circuit 65. The normally conductive stage of the multivibrator 65 is provided by a vacuum tube 161 with the grid of the vacuum tube 161 being connected to the plate of the vacuum tube 160 by a resistor 162 and a condenser 163 connected in parallel therewith. The grid of the tube 161 is also connected to ground by a resistor 164. The multivibrator circuit 65 is a cathode-coupled circuit and the cathodes of tubes 16%, 161 are interconnected and connected to ground by a common cathode resistor 166. The circuitry of the multivibrator 65 is substantially the same as the Schmitt circuit 57 and the description thereof will not be repeated in detail. Suffice it to say that the tube 151 is maintained conducting by the voltage developed across the resistor 164 with the tube 160 cut off, and the tube 166 is maintained cut off by the current flowing in the cathode resistor 166. When the terminal 118 reaches a predetermined positive voltage level, the tube 161 is rendered conductive and the tube 161 is cut 011 to stop the flow of plate current for tube 161. When the voltage level at junction 118 drops to a point below the predetermined positive level necessary to trigger the circuit to its condition where tube 160 conducts, tube 161 is cut off and plate current ceases to flow in the plate circuit of tube 161.

The operation of the adder 511 and the manner in which it controls the Schmitt trigger multivibrator circuit 65 will be best understood by reference to FIG. 6 which is a simplified showing of the adder circuit and the first stage of the Schmitt trigger 65 represented by the vacuum tube 160. As can be seen from FIG. 6, the plate of the output tube 53 of the variable-gain amplifier 4-8 is coupled to the grid of the tube 165 through the resistor 105a and the movable tap 154 of the one-shot multivibrator circuit 53 is coupled to the grid of the tube 166 through the resistor 1139; and the biasing voltage supplied by the voltage dividing circuit comprised of the resistor 114, the potentiometer resistor 113, and the resistor 115, is applied to the control grid of the tube 169 through the resistor 116. The resistors 1115a, 1119 and 116 act as a summing circuit and the algebraic sum of the voltages applied thereto determine the magnitude of the control voltage applied to the grid of the tube 1613 and, in turn, the condition of the Schmitt trigger circuit 65. Preferably, the diode 110 is included in the circuit to allow the condenser 156 to quickly re-establish the charge which is normally main- 1 1 tained thereon when the one-shot multivibrator circuit 53 is in its stable condition.

The tube 161 has in the plate circuit thereof a relay coil 170. The relay coil has a movable switch arm 171 which, when the relay is deenergized, is in engagement with a contact 172 and when energized, is in engagement with a contact 173. The plate circuit of the tube 161 may be connected to the positive side of the power supply either through a circuit completed through the relay arm 171 and the contact 173 or through a circuit which can be completed by closing a switch 174. The switch 174 is a switch which is actuated momentarily to connect the plate of the tube 161 to the positive side of the power supply so that the relay coil 170 will be picked up to actuate the relay arm 171 from its de-energized position to its energized position in engagement with the contact 173. This will maintain the circuit for energizing tube 161. When the tube 161 stops conducting by reason of a triggering signal being applied to the tube 160, the relay coil 170 will drop out and the relay arm 171 will engage the contact 172. Engagement of the relay arm 171 with the contact 172 completes a circuit for energizing a relay 175 having contacts 176 which are broken when the relay is energized. When the contacts 176 are broken, a control operation is performed for stopping the feeding of the sheets. Preferably, the relay 175 has an indicator device 177 connected in parallel therewith.

Preferably, the above circuit is adjusted so that the magnitude of the positive going signal from the variable-gain amplifier i8 is the same magnitude as the signal from the one-shot multivibrator 53. The pulse height, i.e. sig nal magnitude, from the variable gain amplifier 48 may be adjusted by varying the variable resistor 95 in the cathode circuit of the second stage of the amplifier. This adjustment will accommodate various thickness sheets. Without an adjustment, the magnitude of the pulse from the variable gain amplifier 48 would vary with the sheet thickness. Some means for adjusting the relative magnitudes of the pulses from the one-shot multivibrator 53 and the variable-gain amplifier 4B is advantageous if the circuit is to operate on more than one basic sheet thickness.

It will be noted that the pulse magnitude from the variable-gain amplifier 48 is not critical insofar as effecting a triggering of the one-shot multivibrator 53 is concerned. The pulses which efiect the triggering of the one-shot multivibrator 53 are derived from the multivibrator 57. The output of the multivibrator 57 can be set to be of a predetermined magnitude regardless of the magnitude of the input signal which triggers the circuit, and the input can be adjusted so that the circuit 57 is triggered by a pulse signal which corresponds to the minimum sheet thickness to be used with the machine. It will be noted that the variable resistor in the cathode circuit of the triode 145 can be varied to adjust the magnitude of the pulse from the one-shot multivibrator 53.

While the invention has been described with a stream where the'sheet arriving at the sensing station is covered by a single sheet, it will be recognized that the arriving sheet need not be covered or may be covered by several sheets as long as the total thickness is not beyond the range of the transducer. This is true because the sensing circuit means is responsive to changes in stream thickness and not to total thickness.

It will be recognized from the foregoing that the circuitry is responsive to the rate of movement of the ball 24 and that if the ball is very gradually displaced, a weak pulse will occur. It is desirable, therefore, to have a pronounced displacement of the ball so as to provide the necessary pulse upon the arrival of the sheet edge. When light flexible sheets are being handled, the top sheet or sheets will generally drape themselves over the edge of the. covered sheet to provide a sharp rise as shown in FIG. 1A of the application. If, however, the sheets being handled are of relatively stiff material, for example cardboard, the top sheet will not sharply drape itself over the edge of the sheet adjacent the top of the feed table but will have a gradual slope from the edge of the sheet next to the table downwardly to the point where the top sheet engages the table as is shown in FIG. 10. FIG. 10 illustrates this effect on a feed table 10' which does not have the ramp 26. This slope or incline would cause the ball 24 to be displaced gradually rather than sharply and a weak pulse is very likely to result from the circuit. When the ramp 26 is provided, the ramp lifts the top sheet and supports it at a point directly beneath the ball and above the top of the sheet moving to the sensing station and as the sheet moving to the sensing station arrives at the ball, it must move up the ramp 26 and will eiiect a pronounced displacement of the ball 24, as is best understood from considering the enlarged showing in FIG. 9 which shows the leading edge of a covered sheet approaching the ramp.

As indicated previously, the circuit which is responsive to the pulses from the sensing means or from the sensing means and the clock pulses, or both, may take various forms. FIG. 7 schematically indicates another form that the present invention may take. The pulses from the variable-gain amplifier 48 may be applied to one input of an adder circuit and to one input of an AND gate 131. The pulses from the amplifier 55 may be applied to a second input of the AND gate 181 and the AND gate will have an output signal on an output connection 182 connected to the adder circuit 180 when both pulses are present. Since the output of the AND circuit gate is to be of a sense opposite to the sense of the pulse from the variable-gain amplifier 48, the connection 182 preferably includes a one-shot multivibrator 183 which is triggered by the output signal from the AND gate 181 and which provides a pulse of the necessary sense and magnitude to effectively cancel the pulse from the variable-gain amplitier when the latter pulse is due to the presence of a single sheet. The output of the adder is connected to control relay circuitry, as in the first described embodiment.

The pulses in the second described embodiment will effect a triggering of the relay control circuitry to effect a control operation when a pulse from the variable-gain amplifier occurs without any corresponding pulse occurring from the amplifier 56, or if the pulse from the variable-gain amplifier is sufiiciently larger than the pulse from the amplifier 56 that the adder circuit still has an output which will effect a triggering of the relay circuitry. It will be noted that in the above-described circuits, the

clock pulses will not effect a triggering of the relay cir- V cuitry if they occur at a time when there is no pulse from the variable-gain amplifier 48. This condition, however, signals that a sheet is not present when one should be present. The circuitry shown in logic form in FIG. 8 of the application iscircuitry which will also trigger the relay control circuitry if a sheet is absent when a clock pulse occurs.

In FIG. 8, the sheet pulses from the variable-gain amplifier 48 are applied to a Schmitt trigger circuit and to a one-shot multivibrator 191. The Schmitt trigger circuit .199 is set so that whenever the pulse from the variable-gain amplifier 48 reaches a predetermined magnitude, which magnitude preferably corresponds to that of a double sheet, the circuit is triggered to provide a pulse as in the case of Schmitt trigger circuit 65. The output of the trigger circuit 1% is connected to a pulse-responsive control circuit for effecting a control operation in response to a pulse derived when the circuit 1% is triggered;

The one-shot multivibrator 191 is set so that it is triggered from its stable state to its nonstable state each time a pulse is applied thereto. The one-shot multivibrator 191 has two output connections designated respectively by the reference numerals 192, 193. During the transitions of the'multivibrator 191 in response to a triggering pulse, a pulse will appear on the output connection 192 and while the one-shot multivibrator 191'is in an unstable state,.a gating voltage appears on the connection 193 con- 13 nected to one input of an AND gate 194. When the one-shot multivibrator 191 is in its stable state, the gating voltage on gate 194 is such as to pass pulses on a second input connection 195, but when the multivibrator 191 is in its unstable state, the gating voltage on connection 193 is such as to cause the AND gate 194 to block pulses applied to the second connection of the AND gate. The output pulse on the output connection 192 of the multivibrator 191 is applied to the input of an AND gate 197 and will be passed it a gating voltage is applied to an input connection 198 to the AND gate.

The clock pulses in the embodiment of FIG. 8 trigger a one-shot multivibrator 200 and the one-shot multivibrator has an output connection connected to the connection 195 so that when the one-shot multivibrator 2% is triggered in response to a clock pulse, a pulse occurs on the connection 195 during the transition stages of the one-shot multivibrator. The one-shot multivibrator 2% also has an output connected to the connection 198 to control the gating of the AND gate 197. When the one-shot multivibrator is in its stable state, the signal level on connection 198 Opens the gate 197 to pass pulses on input connection 192, but when the one-shot multivibrator 200 is triggered to its unstable state, the signal on connection 198 is such that the pulses on connection 192 will be blocked by the AND gate 197. The outputs of the AND gates 194, 197 are both connected to the pulse-responsive control circuit and whenever an output signal appears from either the AND gate 194 or the AND gate 197, a control operation is eltected.

It will be apparent from the foregoing that if the oneshot multivibrator is not triggered by a pulse from a sheet when a clock pulse occurs, the AND gate 194 is conditioned to pass the pulse from the one shot multivibrator to the pulse-responsive control circuit to effect a control operation. Similarly, the gate 197 will pass the sheet pulse if no clock pulse is present to trigger multivibrator 200. Also, it is apparent that if the clock pulses and the sheet pulses appear simultaneously, both AND gates will be blocked and no control operation will be effected unless the magnitude of the pulse is such as to trigger Schmitt circuit 190.

While in the described embodiment, the pulses derived from the leading edge of the sheet are utilized to analyze the thickness of the sheet and the time of arrival, it will be appreciated by those skilled in the art that the pulses derived from the trailing edge of the sheet could be utilized in a similar manner to analyze the thickness of the sheet material passing the sensing station and the time at which the sheet material passes the sensing station.

In the preferred and illustrated embodiment, the transducer T is a magnetic type of transducer wherein a member of magnetic material which determines the inductance of a coil has a position dependent upon sheet thickness. It will be appreciated that other types of transducers may be utilized. For example, the transducer may be a piezoelectric crystal in which the crystal is stressed by a member which has a position dependent on sheet thickness, or the transducer might essentially comprise means for establishing an electric field across the sheet path at the sensing station with the dielectric constant for the field being varied by changes in sheet thickness. Also the deflection of a movable element may effect the variation of a resistance or capacitance to provide a variable signal which is dependent upon sheet thickness.

It can now be seen that the present invention provides a new and improved sheet-handling machine wherein the leading edge of a sheet arriving at a sensing station eifects the actuation of a sensing element to provide a pulse which has a magnitude dependent upon the thickness of the sheet material arriving and which may be compared or analyzed to determine whether sheets are being properly fed. The height of the pulse may be measured to determine whether or not the sheetmaterial is of proper thickness and the pulse may also be compared with a clock pulse to effect a control operation in the event that a clock pulse does not occur in proper, timed relationship with respect to the pulse from the sheet material. Furthermore, the sensing apparatus uses a sensing element which does not interfere with side registration of the sheet and the sensing apparatus is simple and easily supported in position for effecting the sensing operation. Furthermore, the sensing apparatus is efiective even though the sensed edge of the arriving sheet material is covered by other sheet material which lies between the element which is deflected by the leading edge of the arriving material.

While a preferred embodiment has been described in considerable detail, it is hereby my intention to cover all modifications, construction, and arrangements which fall within the ability of those skilled in the art and within the scope and spirit of the present invention.

Having described my invention, what I claim is:

1. In a sheet-handling apparatus wherein sheets are successively moved along a sheet path past a sensing station disposed along said path, means at said sensing station for sensing a sheet as it passes the station and providing an electrical pulse in response to the passage of an edge of the sheet and having a magnitude which is the function of the rate of change of thickness of said edge as it passes the sensing station, and further means connected to the first-mentioned means for analyzing the magnitude of said pulse and for performing a control operation affecting the movement of said sheets when said pulse is greater than a predetermined magnitude.

2. In a sheet handling apparatus, the structure as defined in claim 1 wherein said further means includes a trigger circuit having a first condition in the absence of pulses and triggered to a second condition when said output pulses have said predetermined magnitude.

3. In a sheet-handling apparatus wherein sheets of sheet material are successively moved along a sheet path, a sensing station along said path for sensing sheets moving thereby and including first means responsive to the thickness of sheet material at said station to provide a signal having a magnitude which is a function of said thickness, first circuit means responsive to said signal and for providing an output pulse having a magnitude which is a function of the rate of the changes of said signal in one direction, pulse-responsive circuit means providing an output signal for performing a control operation when an input pulse is applied thereto having a predetermined magnitude, and connecting means connecting said first circuit means to said pulse-responsive circuit means to apply said output pulse thereto, said predetermined magnitude being greater than the magnitude of said output pulse corresponding to a predetermined normal change in signal.

4. In a sheet-handling apparatus wherein sheets are successively moved along a sheet path to a predetermined position, a sensing station along said path for sensing the passing of sheets and including an element having a position dependent on the thickness of sheet material at said station and first means responsive to the rate of movement of said element to provide an output pulse having a magnitude which is a function of the change in one direction of the thickness of sheet material at said station, pulseresponsive circuit means providing an output signal for performing a control operation when an input pulse is applied thereto of a predetermined magnitude, and means connecting said first means to said pulse-responsive circult means to apply said output pulse thereto as the input pulse of said pulse-responsive circuit means, said predetermined magnitude being greater than the magnitude of a pulse from said first means corresponding to a predeterinined normal change in thickness of said sheet materia 5. In a sheet-handling apparatus wherein sheets are successively moved along a sheet path past a sensing station disposed along said path, means at said sensing station for sensing the passing of a sheet at the station and providing an electrical pulse having a magnitude which is the fund 1 5 tion of the rate of change of thickness of the sheet'material passing the station, and further means connected to the first-mentioned means for analyzing the magnitude and time of said pulses and for performing a control operation when said pulses are out of time and greater than a predetermined magnitude respectively.

6. In a sheet-handling apparatus wherein sheets are moved in succession along a sheet path past a sensing station, first circuit means at said station and responsive to the thickness of sheet material at said station to provide a signal having a magnitude which is a function of said thickness, second circuit means connected to said first circuit means and responsive to changes in one direction of the magnitude of said signal to provide an output pulse when said signal changes, in said one direction due to the arrival of a sheet at said sensing station with the magni tude of said pulse being a function of the change in thickness of the sheet material at said sensing station, and third circuit means connected to said second circuit means for analyzing the time and magnitude of said pulses and performing a control function when said pulses are above a predetermined magnitude and out of time respectively.

7. A sheet-handling apparatus as defined in claim 6 and further wherein said third circuit means comprises pulsegenerating means for generating a clock pulse each time a sheet is to pass said sensing station, control means for performing a control function in response to a signal, and translating means connecting said pulse-generating means and said third circuit means to said control means to provide the input signal to the latter and responsive to the existence in time of an output pulse only for effecting said control operation and including inhibiting means responsive to the co-existence of said clock pulse and output pulse for preventing said output pulse from effecting said control function when said output pulse is below a predetermined magnitude.

8. A sheet-handling apparatus as defined in claim 7 wherein said inhibiting means for preventing said control operation comprises means responsive to the co-existence of a clock pulse and an output pulse for providing a subtract pulse having a sense opposite to said output pulse, and said translating means further includes a summing circuit for algebraically adding said output pulse and said subtract pulse to provide an output signal which is a function of the difference between said output pulse and subtract pulse, said output signal having a magnitude sufiicient to actuate said control means when said output pulse is greater than said predetermined magnitude.

9. In a sheet-handling apparatus wherein a plurality of sheets are moved in succession past a sensing station, sensing means at said station including a sensing element deflected in a first direction by the arrival of a particular edge of the sheet at said station, first circuit means responsive to the deflection of said element in said first direction for providing a pulse, pulse-generating means operated in synchronism with said sheet-handling apparatus and providing a clock pulse at the time said edge is to arrive at said sensing station, means for comparing the time of occurrence of said pulses and for effecting a control operation in response to the occurrence of said output pulse out of time with respect to said clock pulse.

10. In a sheet-handling apparatus wherein sheets are moved in succession along a sheet path past a sensing station, sensing means at said station responsive to the thickness of sheet material therebetween and providing a first output pulse in response to the rate of change in one direction of the thickness of sheet material passing said station, said first output pulse having a magnitude which is a function of the change in thickness control means for performing a control operation, circuit means connecting said sensing means to said control means and applying said first output pulse to said control means to effect said control operation, pulse-generating means for V generating a clock pulse each time a first output pulse is to occur and means connecting said pulse-generating means to apply said clock pulse to said circuit means, said circuit means including means responsive to the existence in time of said first output pulse and said clock pulse and providing an additional pulse having a magnitude and sense opposite to said first output pulse and circuit means for algebraically adding said first output pulse and said additional pulse and providing an output signal when said first output and additional pulses are of different magnitudes, said control means including means responsive to said output signal when the latter has a predetermined magnitude for effecting a control operation.

11. In a sheet-handling machine, sensing means for providing a pulse in response to the movement of a sheet to a predetermined position on a table comprising a magnetic sensing device including a magnetic coil and a movable magnetic member displaceable relative to said coil to nonlinearly vary the inductance of said coil, said coil having an inductance dependent on the position of said magnetic member relative thereto, means supporting said movable magnetic member adjacent said table and in a position relative to said coil dependent on the thickness of the sheet material at said predetermined position, circuit means responsive to changes in said inductance to provide a pulse signal having a magnitude directly dependent upon the magnitude of the displacement effecting the change in inductance, pulse-generating means operated synchronously with said machine and providing a clock pulse whose time of occurrence indicates the time at which a sheet is to arrive at said station, and circuit means responsive to said pulse signal for performing a control operation when said pulse signal is a predetermined magnitude and for comparing the time of said pulse signal with the time of said clock pulse and performing said control operation when said pulse signal is out of time.

12. In a sheet-handling machine, a transducer for sensing the movement of sheets to a predetermined position on a table, a ball of magnetic material adapted to ride on the sheet material at said station and free to move toward and from said table, a magnetic core disposed below the upper surface of the table and having an air gap opposite to said ball, means constraining said ball against lateral movement, and an inductance coil on said core, said core and ball being relatively positioned so that the inductance of said coil varies as a predetermined function of the position of said ball.

13. In a sheet-handling machine, a transducer for sensing the movement of sheets to a predetermined position on a table, a ball of magnetic material adapted to ride on the sheet material at said station and free to move toward and from said table, a magnetic core disposed below the upper surface of the table and having an air gap opposite to said ball, means constraining said ball against lateral movement, an inductance coil on said core, said core and ball being relatively positioned so that the inductance of said coil varies as a predetermined function of the position of said ball, and a ramp rising above the upper surface of said table and disposed between said ball and core.

14. In a sheet handling machine including a feed table along which underlapped sheets are successively moved past a sensing station, means at said sensing station for sensing the passage of an edge of the covered sheet adjacent said table including a deflectahle sheet sensing element disposed immediately above said stream and deflected by a change in position of the top of the stream at said station, a hump rising, from said table below said element at least approximately the thickness of said sheets whereby a pronounced deflection of said element occurs on the passage of a sheet edge over said hump, and means responsive to the rateand magnitude of deflection of said element for providing a pulse which has a magnitude which is a function of change in the thickness of sheet material at said station.

ate-2,301

15. In a sheet handling machine including a feed table along which underlapped sheets are successively moved past a sensing station, means at said sensing station for sensing the passage of an edge of the covered sheet adjacent said table including a deflectable sheet sensing element disposed immediately above said stream and deflected by a change in position of the top of the stream at said station, a hump rising from said table below said element at least approximately the thickness of said sheets, and means responsive to the rate and magnitude of deflection of said element for providing a pulse which has a magnitude which is a function of change in the thickness of sheet material at said station.

16. In a sheet handling machine including a feed table on which underlapped sheets are successively moved past a sensing station, eans at said sensing station for sensing the passage of an edge of a covered sheet including a defiectable sensing element disposed immediately above said stream and deflected by a change in position of the top of said stream at said station, and means responsive to the rate of change of said deflection for providing a pulse as the edge of a covered sheet passes said station, and means for comparing the time of said pulse and for performing a control operation afiecting the movement of said sheets if said pulse is absent at a particular time comprising a clock pulse generator for generating a clock pulse whose time of occurrence is related to the time at which a sheet is to pass said sensing station.

17. In a sheet handling machine, a transducer for sensing the movement of sheets to a station on a table, a ball of material adapted to roll on the sheet material at said station and free to move toward and from said table, and means responsive to the movement of said ball away from said table for providing a signal indicative of the rate of movement of said ball in a direction away from said table and means responsive to the absence of said signal at a predetermined time to perform a control function and the occurrence of said signal in advance of said predetermined time for performing said control function.

18. In a sheet handling machine, a transducer for sensing the movement of sheets to a station on a table, a ball of material adapted to roll on the sheet material at said station and free to move toward and from said table, and means responsive to the movement of said ball away from said table for providing a signal indicative of the rate of movement of said ball in a direction away from said table and means responsive to the magnitude of said signal for performing a control function when the magnitude exceeds a predetermined rate.

19. In a sheet handling machine, means for providing a pulse in response to the movement of a sheet to a predetermined position on a table comprising a magnetic sensing device including a magnetic coil and a magnetic member displaceable relative to said coil to non-linearlly vary the inductance of said coil, said member being a ball which rides on the top of the sheet at said predetermined position, said coil having an inductance dependent upon the position of said magnetic member relative thereto, means supporting said magnetic member adjacent said table and in a position relative to said coil dependent on the thickness of the sheet material at said predetermined position, circuit means responsible to changes in said inductance to provide a signal having a magnitude directly dependent on the magnitude of the displacement effecting the change in inductance, and circuit means responsive to said signal for performing a control operation when said signal is a predetermined magnitude.

20. In a sheet-handling machine, the structure as defined in claim 19 wherein said table includes a ramp disposed below said ball and rising above the surface of the table, said sheets riding up said ramp when moving to said predetermined position.

Reterences Titer by the Examiner UNITED STATES PATENTS 1,946,924 2/34 Allen et al. 340- 2,016,978 10/35 Thomas 340-195 2,058,518 10/36 Schuster 340-195 2,072,236 3/37 Wormser 271-57 2,074,396 3/37 Howe 340-212 2,091,522 8/37 Perry 340-259 X 2,129,230 9/38 ONeil 271-57 X 2,306,211 12/42 Geiss. 2,340,609 2/44 Mestas 340-195 2,357,850 9/44 Reid 271-57 X 2,361,173 10/44 Browne 340-195 2,579,922 12/51 Goldsworthy. 2,700,132 1/55 Kuehne 192-127 X 2,713,134 7/55 Eckweiler 318-19 2,830,191 4/58 McCollom et al. 250-214 2,896,196 7/59 Hartford et al. 340-259 2,963,293 12/60 Klein 271-57 3,046,533 7/62 Torn et al. 340-265 3,114,902 12/63 Tanguy 340-263 FOREIGN PATENTS 661,704 11/51 Great Britain.

1,010,449 6/57 Germany.

NEIL C. READ, Primary Examiner. E. JAMES SAX, Examiner. 

1. IN A SHEET-HANDLING APPARATUS WHEREIN SHEETS ARE SUCCESSIVELY MOVED ALONG A SHEET PATH PAST A SENSING STATION DISPOSED ALONG SAID PATH, MEANS AT SAID SENSING STATION FOR SENSING A SHEET AS IT PASSES THE STATION AND PROVIDING AN ELECTRICAL PULSE IN RESPONSE TO THE PASSAGE OF AN EDGE OF THE SHEET AND HAVING A MAGNITUDE WHICH IS THE FUNCTION OF THE RATE OF CHANGE OF THICKNESS OF SAID EDGE AS IT PASSES THE SENSING STATION, AND FUTHER MEANS CONNECTED TO THE FIRST-MENTIONED MEANS FOR ANALYZING THE MAGNITUDE OF SAID PLUSE AND FOR PERFORMING A CONTROL OPERATION EFFECTING THE MOVEMENT OF SAID SHEETS WHEN SAID PULSE IS GREATER THAN A PREDETERMINED MAGNITUDE.
 9. IN A SHEET-HANDLING APPARATUS WHEREIN A PLURALITY OF SHEETS ARE MOVED IN SUCCESSION PAST A SENSING STATION, SENSING MEANS AT SAID STATION INCLUDING A SENSING ELEMENT DEFLECTED IN A FIRST DIRECTION BY THE ARRIVAL OF A PARTICULAR EDGE OF THE SHEET AT SAID STATION, FIRST CIRCUIT MEANS RESPONSIVE TO THE DEFLECTION OF SAID ELEMENT IN SAID FIRST DIRECTION FOR PROVIDING A PULSE, PULSE-GENERATING MEANS OPERATED IN SYNCHRONISM WITH SAID SHEET-HANDLING APPARATUS AND PROVIDING A CLOCK PULSE AT THE TIME SAID EDGE IS TO ARRIVE AT SAID SENSING STATION, MEANS FOR COMPARING THE TIME OF OCCURRENCE OF SAID PULSES AND FOR EFFECTING A CONTROL OPERATION IN RESPONSE TO THE OCCURRENCE OF SAID OUTPUT PULSE OUT OF TIME WITH RESPECT TO SAID CLOCK PULSE.
 12. IN A SHEET-HANDLING MACHINE, A TRANSDUCER FOR SENSING THE MOVEMENT OF SHEETS TO A PREDETERMINED POSITION ON A TABLE, A BALL OF MAGNETIC MATERIAL ADAPTED TO RIDE ON THE SHEET MATERIAL AT SAID STATION AND FREE TO MOVE TOWARD AND FROM SAID TABLE, A MAGNETIC CORE DISPOSED BELOW THE UPPER SURFACE OF THE TABLE AND HAVING AN AIR GAP OPPOSITE TO SAID BALL, MEANS CONSTRAINING SAID BALL AGAINST LATERAL MOVEMENT, AND AN INDUCTANCE COIL ON SAID CORE, SAID CORE AND BALL BEING RELATIVELY POSITIONED SO THAT THE INDUCTANCE OF SAID COIL VARIES AS A PREDETERMINED FUNCTION OF THE POSITION OF SAID BALL. 